Field of the Invention (Technical Field)
The present invention relates to a low pressure limited overspray handheld aerosol spray gun for spraying a two-component adhesive, a method for spraying a two-component adhesive and a two-component adhesive obtainable by the method.
Description of Related Art Including Information Disclosed Under 37 C.F.R. §§ 1.97 and 1.98
In manufacturing of larger objects, such as matrasses and furniture, adhesives are often applied to fix parts of the large object together. Most adhesives are applied using either air-spray equipment or air-assisted spray equipment.
Airless spraying involves using pressure to force a fluid to be sprayed through a small orifice. Airless spray equipment is often operated at higher pressures than air-spray- or air assisted-spray equipment. Operating pressures of airless spray systems are typically up to 50,000 kPa (−500 bar). Air-spray uses pressurized air to spray adhesives. Operating pressures are typically up to 1600 kPa (−16 bar). In view of operating pressure, and in view of adhesives used, air-spray and airless spray methods are at least difficult to combine. Methods and products for applying a layer of adhesive onto a surface wherein the method comprises spraying the adhesive airlessly are known in the prior art. Likewise air pressurized products and methods are known.
Prior art methods and spray guns, and especially air-assisted spray equipment, suffer from a phenomenon called over-spray. It is noted that spraying inherently relates to having an adhesive to be air borne. Under ideal circumstances, using, e.g., a dedicated and sophisticated fully automated equipment, which may have one spray gun or a series of parallel spray guns, at a fixed distance from a surface to be sprayed an amount of overspray may be limited to less than about 10% of a total amount of adhesive applied. As the sprayed material relates to an adhesive an end result is that eventually all items close by and typically a surrounding environment is covered with a layer of adhesive. More serious is that in view of labor conditions employees are exposed to air-borne adhesives. Of course the overspray is also a waste of materials per se.
A measure that could reduce an amount of adhesive in the air is to actively remove air borne adhesive by suction/ventilation. Apart from the energy and equipment costs such may also involves heating/cooling fresh air being supplied. Furthermore, it also determines a selection of a physical location of spraying to a location where active ventilation is provided; typically spraying cannot be performed at any given location, e.g. where a surface to be sprayed is located. In other words, such is unwanted.
It is noted when the spray gun is handheld the situation is much worse, especially in terms of amount of overspray. Under ideal circumstances, e.g., a fixed distance between the spray gun and object to be sprayed, a fixed pressure, etc. less than 20% overspray (in relation to a total amount applied) is obtainable. In practice more than 30% of the amount applied is over sprayed, and typically more than 40%.
Another issue with airless systems is a phenomenon called tailoring. At the edge of a spraying pattern a relatively larger amount of adhesive is deposited. If the adhesive is colored, which is typically the case, such can be observed as a thicker or more intense colored line. A distribution of adhesive is not even over the surface, e.g., in terms of amount of adhesive per unit surface, which is unwanted.
In case of an air-spray system the adhesive is not homogeneously distributed over a surface to which the spray is applied. Typically there is much more adhesive at the center of the surface compared to the edges thereof. Also a lot of overspray, beyond the edges, is present.
For two-component adhesives good mixing of the two components may be an issue as well. Mixing does not only relate to intimately combining the two components, but also to securing a required ratio of components in the mixed adhesive. Typically one component is provided in a relatively large amount and the other in a relatively small amount. Such is even more complex if a relatively large area needs to be covered with an adhesive.
Other disadvantages for pressurized air systems are as follows. It is noted that pressurized air itself also contributes considerably to costs of applying adhesive, especially if more complex equipment is needed. Also, prior art methods typically make use of rather complicated equipment, especially air assisted spray equipment. Such systems are rather voluminous, complex and costly.
As an amount of adhesive to be applied at a given moment in prior art systems is typically much smaller than a content of a container there is a risk that the component may clog, block a tube, etc. Such requires cleaning of the equipment.
The prior art equipment is typically (somewhat) difficult to handle, e.g., in terms of relocating, and replacing feed stock. Also, in view of complexity, such systems are at a certain distance from a location where the adhesive is being applied; inherently such involves some further risks, e.g., clogging of tubing, less control at the location of application, etc.
In an example DE 33 360 53 A recites a 2-component spray gun with two spray heads, in which the main component is atomized by the airless spray method and the hardener component is atomized by the compressed-air spray method. A high pressure is used to spray the two components. As a result, airborne particles are formed which spread throughout a given location of application and a spray pattern is not well controlled.
U.S. Pat. No. 4,928,884 A recites a fluid assist airless spray nozzle for spraying a plural component spray system with a nozzle plate having an airless discharge orifice located therein for spraying a first component of the plural component system as, for instance, a resin component. A first fluid discharge orifice is located on one side of the airless discharge orifice and a second fluid discharge orifice is located on the other. Outboard of the first fluid discharge orifice is a first gas discharge orifice and outboard of the second fluid discharge orifice is a second gas discharge orifice. The system is considered rather complicated, having various of the above risks, such as airborne particles, and typically not providing an adequate spray pattern.
In view of the disadvantages of the prior art systems there is a need for an improved low pressure 2-K handheld spray gun which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages.